Unresolved problems in graser development

Although it has been recognized for two decades that the Mossbauer effect offers the possibility of stimulated emission from nuclear states, the contradictory requirements of an intense pump and a relatively undisturbed solid host continue to frustrate attempts to devise a workable gamma ray laser system. The basic requirement for gain and some recent proposals for satisfying it are reviewed identifying the difficulties each proposal presents. Finally, the kinds of information, experience, and ideas that may enable further progress are suggested.